A general multi-blade centrifugal blower is shown in FIG. 23. An impeller wheel 7a of the blower is accommodated in a casing 7b, and provided with multiple blades 71 which are arranged around the central line 70 of a rotation shaft (not shown) of the blower. The blower sucks air through a suction portion 74 disposed at the side of one rotation-shaft-direction end of the blower, and blows air toward a diameter-direction outer side of the blower.
The impeller wheel 7a is provided with a large inner/outer diameter ratio and a large blade width (which is dimension in rotation shaft direction of impeller wheel 7a). Therefore, the space which is between the adjacent blades 71 and near the suction portion 74 will become an inefficacious zone, where air flowing direction abruptly varies from the rotation shaft direction to the diameter direction to cause a large eddy so that a main air flow does not flow.
Various proposals are made in order to decrease the inefficacious zone and uniform the outlet (of impeller wheel) air flowing speed throughout the blade 71 for the sake of work-capacity increase, efficiency improvement and noise reduction.
In a multi-blade centrifugal blower with reference to JP-61-107000A, the blade is provided with a cross section shape which is inclined from the side of a boss portion (i.e., main plate) toward the side of a support ring (i.e., side plate) in a direction contrary to a rotation direction of the impeller wheel, in order to exert a force in the rotation direction to air to reduce the inefficacious zone.
In a multi-blade centrifugal blower with reference to JP-2001-115997A, a main plate and a side plate are sequentially twisted, in a state where a blade outlet portion of the side of the main plate is positioned at a rotation-direction front side with respect to the blade outlet portion of the side of the side plate. Thus, an inlet angle and an outlet angel which are different from each other are provided.
In a multi-blade centrifugal blower with reference to JP-4-5500A , the blade of the side of a side plate is bent in the rotation direction with respect to the rotation shaft direction of the blower. That is, a bend portion is provided.
However, in the multi-blade centrifugal blowers with reference to JP-61-107000A and JP-2001-115997A, fluid inflow from the rotation shaft direction is not considered, so that little fluid flows into the space which is between the adjacent blades and near the suction portion. Therefore, the improvement effect is petty.
In the multi-blade centrifugal blower with reference to JP-4-5500A, the bend portion deteriorates operation performance and noise even though the fluid inflow from the rotation shaft direction is considered.